DPF and that whole clean diesel is a major pain once things start happening. A bad thermostat leads to a clogged DPF quicker so see what your coolant temps are at while on he highway, should be around 85-88 degrees i believe. Anything under 75 is bad thermostat.
There are ways to eliminate the DPF and Urea injection with a tune for around $2000 if you wanted to keep the x5. I read after 100k, trans fluid change is definitely needed.
Mine is a 2011 35d with almost 110k on it.

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2011 35d